A seismic survey typically involves deploying seismic source(s) and seismic sensors in a survey area. The seismic sources generate seismic waves, which propagate into geological formations crating pressure changes and vibrations in the formations along their way. Changes in elastic properties of the geological formation scatter the seismic waves, thereby changing their direction of propagation and possibly other properties. A part of the scattered waves reaches the seismic sensors, where seismic signals caused by the interaction of these waves with the seismic sensors are detected and possibly recorded.
Marine seismic surveys may be carried out in a variety of manners. For example, a number of sources and seismic sensors may be towed by a propelled vessel. The seismic sensors may be arranged in one or more streamers to create a line or a 2D grid of seismic sensors. Alternatively, the seismic sensors are deployed on the sea floor, for instance in the form of seismic nodes sometimes referred to as ocean bottom nodes.
US pre-grant publication 2012/0069702 describes a marine seismic survey system using an autonomously or remotely operated vehicle. Such a system may include a water vehicle. The water vehicle may be deployed to a desired position for seismic surveying. Upon positioning, a seismic source that is towed behind the water vehicle may be detonated to generate acoustic waves that propagate through the ocean bottom surface and into the strata beneath the ocean bottom surface. The water vehicle may be equipped with an onboard GPS device.
Time-lapse surveys generally require that a survey is repeated after a certain amount of time has evolved. Time-lapse signals reflect differentials between two or more surveys that result from changes in the survey results over time. The sensitivity of a time-lapse survey to changes in the geological formations depends on the repeatability of the acquisition. The smaller the variation in acquisition conditions is, the more sensitive the time-lapse survey becomes to small changes within the geological formations that are being investigated.